In wireless Orthogonal Frequency Division Multiple Access (OFDMA) communication systems, the transmitting power of each mobile station needs to be maintained at a certain level to achieve desired channel quality and to maximize system capacity. In a Close Loop Power Control (CLPC) mechanism, the transmitting power of a mobile station is controlled by a Transmit Power Control (TPC) command transmitted from a serving base station to the mobile station. The serving base station periodically monitors uplink channel quality of the mobile station, and in response, sends TPC commands for periodic transmitting power adjustments for the mobile station. Uplink channel quality of the mobile station can be derived or estimated by the serving base station based on the reported downlink channel measurements from the mobile station. For example, in Time Division Duplex (TDD) systems, uplink channel condition can be derived from downlink channel measurement due to channel reciprocity. On the other hand, in Frequency Division Duplex (FDD) systems, uplink channel condition can be estimated from downlink channel measurement by exploiting channel correlation between downlink and uplink channels.
FIG. 1 (Prior Art) is a signal diagram that illustrates operation of a conventional uplink power control scheme in a wireless OFDMA system 10. Wireless OFDMA system 10 comprises a serving base station BS11 and a mobile station MS12. In a signal diagram such as FIG. 1, time proceeds from top to bottom in the diagram. As illustrated in FIG. 1, serving base station BS11 first allocates a fast feedback channel (FFBCH) 14 by transmitting a first feedback allocation Advanced-MAP information element (FA-A-MAP-IE) 13 to MS12. FA-A-MAP-IE 13 decides the periodicity of FFBCH 14, which in turn determines how frequently BS11 tracks any uplink channel variation. Mobile station MS12 then measures and reports downlink channel information via the allocated FFBCH 14. The reported downlink channel information is used by base station BS11 to estimate uplink channel quality such as the signal to interference plus noise power ratio (SINR) of the uplink channel. Based on the estimated channel quality, BS11 derives power level of the uplink channel. BS11 is then able to determine whether there is any channel variation and whether a power adjustment is needed in response to the channel variation.
If a power adjustment is needed, then a power offset is delivered to MS12 via an uplink power adjustment (AAI-UL-POWER-ADJ) message 15. AAI-UL-POWER-ADJ message 15 is one of the downlink MAC control message signaled to a specific mobile station. AAI-UL-POWER-ADJ message 15 provides a large power jump to adapt to the detected channel variation quickly. As illustrated in FIG. 1, when BS11 observes a huge power gap in the uplink, BS11 would most likely also want to monitor any upcoming channel variation more closely. Therefore, in addition to AAI-UL-POWER-ADJ message 15 that is transmitted to MS12, BS11 also transmits a second FA-A-MAP-IE 16 to reconfigure FFBCH 14. For example, FA-A-MAP-IE 16 may shorten the periodicity of FFBCH 14 such that BS11 is able to monitor the uplink channel more frequently. It would be great to combine these two messages to save signaling overhead without requiring extra resource.